Low-twist tensioning of boron filament

ABSTRACT

A method for continuously winding high-strength, high-modulus filament onto a takeup spool comprising tensing the filament between a pair of opposed plate members having abrasion resistant planar contact surfaces aligned parallel to both the axis of filament travel and each other whereby the twist introduced to the filament is less than one turn per 10 feet of length.

United States Patent Inventors Donald K. Kuehl Manchester; Raymond C.Smart, Hazardville, both of Conn. App]. No. 879,058 Filed Nov. 24, 1969Patented Jan. 4, 1972 Assignee United Aircraft Corporation EastHartford, Conn.

LOW-TWIST TENSIONING 0F BORON FILAMENT 6 Claims, 2 Drawing Figs.

US. Cl 242/149 R, 117/106 R Int. Cl ..B65h59/22, C23c 11/00, C23c 13/00Field of Search 242/ 149, 147,150, 1, l8, 54;117/106, 201, 69; 57/1, 2,3,

Primary Examiner-Stanley N. Gilreath Attorney-John D. Del PontiABSTRACT: A method for continuously winding highstrength, high-modulusfilament onto a takeup spool comprising tensing the filament between apair of opposed plate members having abrasion resistant planar contactsurfaces aligned parallel to both the axis of filament travel and eachother whereby the twist introduced to the filament is less than one turnper 10 feet of length.

Pmmmm 4197: 3,632,063

JQBKK- LOW-TWIST TENSIONING OF BORON FILAMENT BACKGROUND OF THEINVENTION The production of high-strength and high-modulus reinforcingfibers of small diameter, such as, for example boron filaments, presentsproblems which are unique and generally unknown to the textile industry.There are generally three types of processes for producing high-strengthhigh-modulus filaments. In one, a substrate characterized by relativelyhigh ductility, such as tungsten, is converted by deposition of acoating material to a continuous fiber characterized by high rigidity,such as boron. In the second, a filament characterized by highductility, such as organic precursor materials, is subjected to heattreatment and is also converted to a fiber characterized by highrigidity, such as graphite. In the third, a filament such as sapphire isdrawn from a melt. In all cases, the filament length extending betweenthe converted fiber takeup spool and the unconverted fiber feeding meansacts as a filament with a free end in that the ductile portion isrelatively free to rotate or twist due to any torque applied on theconverted rigid portion; where a torque is so applied there is thusimparted a residual twist to the converted filament. Because of theirstrength and stiffness, it is necessary to wind such filaments onrelatively large diameter spools under considerable tension in order toprevent both breakage and slippage during handling and shipping.Unfortunately, most types of equipment normally used to impart tensionto filaments during winding are inadequate for use with filamentsundergoing conversion from a filament characterized by ductility to afilament characterized by rigidity since they introduce twist to thefilament and also normally result in excessive wear from abrasion. Theformer result is particularly troublesome since, once twist isintroduced, it will be retained until the filament is cut and thenrecovery is rapid unless restrained. A typical consequence, where thefilament is used as matrix reinforcement in the making of compositetapes, is to curl the product tape and render it virtually useless.

Although the desirability of producing a filament such as boron withzero or an acceptably low residual twist is recognized, the means isaccomplish the same are immanifest. Of course, low or zero twist can beachieved by twist removal during unwinding but it will be recognizedthat this is a slow and expensive process. Again, low or zero twistfiber can be produced by eliminating all tensioning restraints, but thisresults in such a loose spool that filament recovery is difficult andexpensive. It is thus recognized that the basic requirement to be met isto continuously provide suitable tension for winding of stifffilamentary material without simultaneously imparting torque thereto.

Most existing equipment, although suitable for providing tension, doesnot reliably meet the second, no-twist, requirement. Opposed rotatingwheels between which the filament passes, for example, do not introducetwist when the wheels are retarded only if the wheels can be maintainedin exact alignment. Unfortunately, even if initial alignment isachieved, it cannot practicably be maintained since abrasive wear andother forces tend to destroy the alignment very rapidly and cause twistintroduction. Capstan-type tensioners inherently produce torque whichcan be minimized only by using an uneconomically large wheel, withabrasion and wear undiminished as a problem. Multiple-wheeled tensiondevices have been operated with no twist, but are found to be difficultto thread, difficult to adjust to proper tension and susceptible toabrasion and wear.

SUMMARY OF THE INVENTION The present invention relates in general to ameans for handling filaments and more particularly to a means forimparting tension, while simultaneously preventing the introduction of asignificant amount of twist thereto, to high-strength, highmodulusfilaments during spool takeup while the filament is being converted froma relatively ductile state, It has been found, In the production ofboron filament of approximately 4 mils diameter in a process such asthat disclosed in copending application Ser. No. 6l8,5l l filed Feb. 24,I967, by Rice and owned by the present assignee, that a twist of greaterthan one turn per 10 feet of filament is significant enough to renderthe filament unacceptable for most applications.

The present invention contemplates the provision of means for uniformlyapplying transverse and directly opposed pressure to the movingconverted filament upstream of the takeup spool. Abrasion-resistantplanar surfaced members are precisely aligned parallel to the filamentaxis to apply the pressure and provide sufficient tension withoutcreating twist.

BRIEF DESCRIPTION OF THE DRAWINGS In the detailed description whichfollows, it will be convenient to make reference from time to time tothe drawings in which:

FIG. 1 is a simple sketch, taken in elevation, of a typical tensiondevice in use in a boron filament production system; and

FIG. 2 is an elevational view of a modification of the tension deviceshown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1, asupply spool 10 of tungsten filament 12 is drawn through a suitablevertical boron deposition chamber 14 such as described in the aforesaidcopending application. The emerging boron-coated filament I6 is pulledonto a takeup spool 18 after passing through a tension device 20. In atypical operation, the boron filament is 4 mils in diameter, the takeupspool is from 3 to 14 inches in diameter, with approximately 8% inchespreferred and suitable winding tension is 15 to 200 grams, preferably 30to 60 grams.

The tension device shown in FIG. 1 comprises a fixed plate member 22 anda movable plate member 24. Both plate members are provided with abrasionresistant mounts 26 and 28 having facing surfaces 30 which are planar inconfiguration. Typically these mounts 26 and 28 have been ground carbideplates, securely mounted on their respective plates 22 and 24 so thatwhen the desired pressure is applied to the boron filament, the facingsurfaces 30 will be precisely parallel. As will be appreciated, otherhard, smooth, abrasion-resistant material in lieu of carbide can be usedfor a mount, such as the ceramics including boron, boron nitride andalumina. The movable plate 24 is pivotally disposed on a pin 32 and isprovided with means, such as the weight 34, to pivot it therearound tobring its mount 28 to a position of alignment with the other mount 26while applying the desired transverse pressure to the filament pinchedtherebetween. It has been found that alignment, that is parallelism,between the surfaces 30 is critical, the permissible angular deviationbetween the two surfaces or between one of the surfaces and the filamentaxis being such that the tangent of the angle cannot be greater than thefilament diameter divided by the length of the contact surface. Thus,for a 4-mil boron fiber and mounts having a one inch contact surface,the maximum permissible angular deviation is approximately 13 minutes.It should be noted that both the fixed and movable plates are adjustablein a direction perpendicular to the planar surfaces 30 so as toaccommodate filaments of varying diameters as well as adjustable in adirection parallel to the planar surfaces 30 so as to present freshportions of the surfaces 30 to the filament 16.

A modified tension device is shown in FIG. 2 with a movable plate 40being pivotally supported by a pair of links 42 and 44 connected to fourpivot pins 46, 48, 50 and 52. With the weight 54 provided as shown,there is provided continuing alignment of the facing surfacesindependent of filament diameter. The fixed plate 56 is made adjustableby a pair of horizontally disposed screws 58.

It will be appreciated by those skilled in the art that otherconfigurations will be suggested by the present disclosure. It isrecognized for example that the moving plate can be mounted on alignmentrails for transverse movement with horizontal pressure being applied bysuitable means such as a spring or a pneumatic or hydraulic actuator orby weights. So long as the opposed wiremcontacting surfaces are parallelto both the filament axis and each other and impart the requisitetension thereto as described hereinabove, wound fibers with less thanone turn per 10 feet will be achieved. It has been found that contactlengths of one-eighth to 5 inches will perform satisfactorily althoughlengths of one-half to 1 inch are preferred. in order to preventchipping of the mounts or breakage of the filament, the leading andtrailing edges of the wire-contacting surfaces are rounded to a minimumradius of one sixty-fourth inch but preferably to one thirty-second toone-eighth inch.

In practice, with a system such as that shown in FIG. 1, boron filamentproduced at from 800 to 850 feet per hour was wound on the takeup spoolwith twist of less than one-tenth of a turn per feet. When opposedrotating wheels were used, while inducing the same level of tension asthe inventive device, they imparted up to nine turns per 10 feet oflength with the average being approximately at between four and fiveturns per 10 feet.

It should be understood that while the present system has been describedin relation to the production of filamentary boron, the concept pertainswith regard to other similar highstrength, high-modulus filaments suchas silicon carbide, silicon nitride, silica, sapphire or graphite.

While the invention has been described in connection with specificembodiments, numerous modifications may be made and it will beunderstood that the true spirit and scope of the invention is set forthin the appended claims.

What is claimed is:

1. In a method for continuously winding filament onto a takeup spoolduring conversion from a filament characterized by high ductility to afilament characterized by relatively high rigidity, the improvementwhich comprises:

tensing the filament by passing it between a pair of opposed platemembers upstream of said spool, said plate members havingabrasion-resistant planar contact surfaces aligned parallel to both theaxis of filament travel and each other whereby the wound filament willbe imparted with a twist of less than one turn per 10 feet of length.

2. The method of claim I wherein said contact surfaces deviate from trueparallelism with the filament axis by an angle not more than one whosetangent is the quotient obtained by dividing the diameter of thefilament by the length of the contact surfaces.

3 The method of claim 2 wherein said filament is tensed by maintainingone of said plate members relatively fixed with its contact surfaceagainst the moving filament and urging the contact surface of the otherof said plate members in a direction toward said one plate member intofrictional engagement with said filament.

4. The method of claim 3 wherein said filament is selected from thegroup consisting of boron, silicon carbide, silicon nitride, silica,sapphire and graphite.

5. The method of claim 3 wherein said filament is boron and is tensed to15-200 grams.

6. A method for winding filamentary boron during production wherein afilamentary substrate of relatively high ductility is coated with boroncomprising:

winding a continuous strand of the boron filament onto a takeup spool,said spool rotating to pull said filament therearound frictionallyengaging said filament between a pair of opposed plate members upstreamof said spool, said plate members having abrasion resistant planarcontact surfaces aligned parallel to both the axis of filament traveland each other whereby there is imparted to the filament a tension offrom ,15 to 200 grams and the twist introduced is less than one turn per10 feet of length.

1. In a method for continuously winding filament onto a takeup spoolduring conversion from a filament characterized by high ductility to afilament characterized by relatively high rigidity, the improvementwhich comprises: tensing the filament by passing it between a pair ofopposed plate members upstream of said spool, said plate members havingabrasion-resistant planar contact surfaces aligned parallel to both theaxis of filament travel and each other whereby the wound filament willbe imparted with a twist of less than one turn per 10 feet of length. 2.The method of claim 1 wherein said contact surfaces deviate from trueparallelism with the filament axis by an angle not more than one whosetangent is the quotient obtained by dividing the diameter of thefilament by the length of the contact surfaces.
 3. The method of claim 2wherein said filament is tensed by maintaining one of said plate membersrelatively fixed with its contact surface against the moving filamentand urging the contact surface of the other of siad plate members in adirection toward said one plate member into frictional engagement withsaid filament.
 4. The method of claim 3 wherein said filament isselected from the group consisting of boron, silicon carbide, siliconnitride, silica, sapphire and graphite.
 5. The method of claim 3 whereinsaid filament is boron and is tensed to 15-200 grams.
 6. A method forwinding filamentary boron during production wherein a filamentarysubstrate of relatively high ductility is coated with boron comprising:winding a continuous strand of the boron filament onto a takeup spool,said spool rotating to pull said filament therearound frictionallyengaging said filament between a pair of opposed plate members upstreamof said spool, said plate members having abrasion resistant planarcontact surfaces aligned parallel to both the axis of filament traveland each other whereby there is imparted to the filament a tension offrom 15 to 200 grams and the twist introduced is less than one turn per10 feet of length.